System to control and condition the supply of natural gas to bi-fuel engines

ABSTRACT

Embodiments of the present invention include a method and computer readable memory for supplying conditioned natural gas to dual fuel engines. Some embodiments of the present invention include an apparatus and process for controlling and optimizing the heating value or BTU per cubic foot of gas (BTU/cf) of the natural gas substituted for diesel fuel in the operation of transport vehicles and field equipment such as generators.

CROSS-REFERENCE TO RELATED APPLICATION

The present application, pursuant to 35 U.S.C. 111(b), claims the benefit of the earlier filing date of provisional application Ser. No. 62/118,984 filed Feb. 20, 2015, and entitled “Natural Gas Supply System for Providing Conditioned Natural Gas to Dual Fuel Engines” and provisional application Ser. No. 62/191,635 filed Jul. 13, 2015, and entitled “Providing Conditioned Natural Gas to Dual Fuel Engines.”

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to an apparatus and process for supplying conditioned natural gas to dual fuel engines. More specifically, the present invention includes an apparatus and process for controlling and optimizing the heating value or British Thermal Units per cubic foot of gas (BTU/cf) of the natural gas substituted for diesel fuel in the operation of transport vehicles and field equipment such as generators.

Description of the Related Art

Cars, trucks, boats, locomotives and other commercial vehicles, as well as generators, are generally fueled by gasoline or diesel fuel. The air pollution problems associated with the reliance on fossil fuels for fueling these engines are well known and have led to various regulations that are aimed at reducing the amount of pollutants discharged into the atmosphere.

In recent years, expanded petroleum exploration and development has led to an increased supply of natural gas. Increasing supplies of natural gas, together with the impending tightening of emissions regulations are key factors in the drive to use natural gas as a fuel of choice for the automobiles, trucks, boats, locomotives and diesel equipment used at field sites. Natural gas has the capability of producing less air emitted pollutants, producing less carbon dioxide (CO₂), particulate matter, oxides of sulfur (SO_(x)) and oxides of nitrogen (NO_(x)) from combustion. Furthermore, natural gas is less expensive than diesel.

The use of dual fuel diesel technology, where diesel engines are adapted to utilize natural gas in co-combustion with diesel fuel, provides flexibility in power delivery while reducing the amount of diesel fuel used. These types of systems are referred to as dual fuel or bi-fuel engines. Natural gas fuel can be substituted for diesel fuel in varying proportions according to an engine's operating conditions. In addition, natural gas is available from multiple sources as Liquefied Natural Gas (LNG), Compressed Natural Gas (CNG), Pipeline Gas (PG), or as field gas, so that the use of natural gas at a field site greatly reduces cost, transportation and emissions.

A need exists for an improved means of dynamically optimizing combustion efficiency and the substitution rate of natural gas for diesel in dual fuel engines.

SUMMARY OF THE INVENTION

The present invention relates to a method and apparatus for conditioning the supply of natural gas to dual fuel engines. Embodiments of the present invention include an apparatus and process for controlling and optimizing the quantity, the timing, and the heating value or British Thermal Units per cubic foot of gas (BTU/cf) of the natural gas substituted for diesel fuel in the operation of transport vehicles and field equipment such as generators.

One embodiment of the present invention is a dual fuel engine natural gas enrichment unit including: a) a natural gas source having a known caloric value per cubic foot; b) a liquefied petroleum gas tank filled with a liquefied petroleum gas having a higher caloric value per cubic foot than the natural gas source; c) an enrichment injector; d) a mixing chamber; and e) an enrichment control unit in communication with the enrichment injector, wherein the enrichment control unit instructs the enrichment injector to inject a calculated quantity of the liquefied petroleum gas into the mixing chamber containing the natural gas source to increase the caloric value per cubic foot of the natural gas source to a desired caloric value per cubic foot; whereby the natural gas source is enriched to a calculated desired caloric value per cubic foot for injection into the duel fuel engine.

A second embodiment of the present invention is a natural gas supply and conditioning system for engines including: a dual fuel engine that burns diesel fuel and natural gas having an engine sensor that monitors at least one engine operating parameter; b) an electronic control system in constant communication with the engine sensor, wherein the electronic control system calculates an optimum caloric value of a natural gas for substitution of a calculated amount of diesel for the dual fuel engine operating at a selected engine parameter; c) a diesel fuel supply; and d) a natural gas enrichment unit having (i) a natural gas supply, (ii) a tank of liquefied petroleum gas filled with a liquefied petroleum gas having a higher caloric value per cubic foot than the natural gas supply, (iii) an enrichment injector; and (iv) an enrichment control unit in communication with the electronic control system and the enrichment injector, wherein the enrichment control unit instructs the enrichment injector to inject a calculated quantity of the liquefied petroleum gas into a mixing chamber containing the natural gas supply to increase the caloric value per cubic foot of the natural gas source to the optimum caloric value per cubic foot.

Yet another embodiment of the present invention is a method for regulating the natural gas used to fuel a dual fuel engine comprising: dynamically determining one or more engine operating parameters; mapping data related to the engine operating parameters with predetermined engine performance data to calculate an optimal natural gas caloric value and substitution ratio of natural gas to diesel fuel under a selected operating condition of the engine; enriching a natural gas source by injecting the natural gas source with a calculated quantity of liquefied petroleum gas to generate an enriched natural gas having the calculated optimal natural gas caloric value; and automatically injecting a desired quantity of the enriched natural gas into the dual fuel engine in accordance with the calculated optimal natural gas substitution ratio.

The engine operating parameters can be stored in a computer readable storage medium. The engine operating parameters include speed of the engine, a speed of a vehicle to which the engine may be connected, a load of the engine, a temperature of intake air directed to the engine via an intake passage, a temperature of ambient air, a temperature of exhaust emitted by the engine, combustion efficiency, and a quantity of non-combusted methane and/or like operating

The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic of a dual fuel engine with an electronically controlled natural gas fuel supply and conditioning system.

FIG. 2A is a schematic of a first embodiment of the natural gas enrichment unit shown in FIG. 1.

FIG. 2B is a schematic of another embodiment of the natural gas enrichment unit shown in FIG. 1.

FIG. 3 is a flowchart illustrating a process for monitoring engine operating conditions and calculating the timing, amount and optimal heating value for the natural gas entering the air inlet manifold in accordance with an embodiment.

FIG. 4 is a flowchart illustrating a process for enriching natural gas in a dual fuel engine in accordance with an embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention include an apparatus and process for controlling and optimizing the heating value or British Thermal Units per cubic foot of gas (BTU/cf) of the natural gas substituted for diesel fuel in the operation of boats, locomotives, over-the-road transport vehicles, and field equipment such as generators, as well as a method and computer readable memory for supplying enriched natural gas to dual fuel engines.

In most dual fuel systems, the natural gas fuel in gas phase is introduced into the air intake system of the engine. Diesel fuel, on the other hand, is introduced directly into the combustion chamber at the end of the compression stroke. The two fuels blend together and are ignited by compression. Diesel fuel and natural gas have distinctly different combustion properties. For example, natural gas has a significantly higher ignition temperature of about 1103° F. than diesel fuel that ignites at a temperature of about 410° F. Many factors affect combustion efficiency and the relative completeness of combustion of the two fuels.

Diesel engines are designed to burn 100% diesel fuel, but it is cheaper and reduces the environmental footprint to run an engine that can substitute natural gas for a certain percentage of the diesel fuel. Each diesel engine has its own fuel burn requirements in order for the engine to sustain a set power. For example, an older engine may perform less efficiently than a new engine. However, all dual fuel engines must burn at least some diesel fuel in the engine fuel mixture in order for the engine to run smoothly and efficiently.

Currently available dual fuel engines compensate for the engine fuel requirements based upon engine RPM, engine load and a steady state flow of natural gas at a constant caloric content or heating value. The caloric content or heating value of a fuel is given as the BTU per cubic foot of gas (BTU/cf). Since engines require a different BTU/cf for every RPM and engine load, using a fixed BTU/cf to calculate and set the substitution rate for natural gas minimizes the substitution rate at certain engine loads and results in a less efficient engine fuel burn. Inefficient natural gas combustion produces non-combusted methane emissions released into the atmosphere.

A schematic of one embodiment of a duel fuel engine system 100 known to optimize natural gas substitution, engine efficiency and fuel combustion is shown in FIG. 1. The engine system 100 includes a dual fuel engine 110, an engine sensor mechanism 120, an electronic control system 130, a supply of diesel fuel 140, and a natural gas enrichment unit 200.

The Dual Fuel Engine Sensor and Communication System

It is highly desirable to optimize the natural gas substitution rate for each duel fuel engine. Although natural gas/diesel duel fuel engines need at least a minimal diesel component for proper combustion, an optimum fuel ratio that maximizes the substitution rate of natural gas can result in about 70% natural gas to 30% diesel at high power loads.

In order to maximize the substitution of natural gas for diesel in a dual fuel engine, the engine will be continually monitored by an engine sensor mechanism 120 that will provide engine data such as fuel flow, power load, RPM and cylinder temperature to the electronic control system 130. The electronic control system 130 receives the engine data from the engine sensor mechanism 120 of the dual fuel engine 110. The electronic control system 130 then calculates the optimum timing, quantity, flow and BTU/cf content of the natural gas to be delivered to the engine from the received engine data.

Since the optimum caloric content (BTU/cf) of the natural gas entering the air intake system of the dual fuel engine will vary with the operating conditions of the engine and certain environmental conditions such as barometric pressure (altitude) and ambient temperature, the dual fuel engine must be constantly monitored. The electronic control system 130 constantly communicates to the natural gas enrichment unit 200 the calculated optimum quantity, flow and BTU/cf content of the natural gas.

The Gas Enrichment Unit

The natural gas source 220 available for the dual fuel engine may be from a variety of sources such as Liquefied Natural Gas (LNG), Compressed Natural Gas (CNG), or even Pipeline Gas (PG). The BTU/cf of LNG and CNG is typically 1000±50 BTU/cf, whereas the reported range for North American field gas is 950-1,650 BTU/cf with an average reported value of about 1025±25 BTU/cf.

The most common source of natural gas used for trucks, boats, and locomotives is LNG or CNG with a BTU/cf of 1000±50, which is often less than the desired BTU/cf calculated for the optimum performance of a dual fuel engine. The natural gas source 220 available for dual fuel engines used at a field site may also be from Liquefied Natural Gas (LNG), Compressed Natural Gas (CNG), or sometimes Pipeline Gas (PG). If the natural gas source is PG the BTU/cf for the natural gas source 220 delivered to the enrichment unit 200 is typically adjusted to be about 10-50 BTU/cf below the lowest calculated BTU/cf needed for the efficient running of that particular dual fuel engine 110.

The electronic control system 130 dynamically provides the appropriate instructions to the gas enrichment unit 200 to adjust the caloric value of the natural gas source 220 to the desired BTU/cf needed for the efficient running of that particular dual fuel engine under the specific operating conditions of that engine. Embodiments of the gas enrichment unit 200 are schematically illustrated in FIGS. 2A and 2B. The gas enrichment unit 200 illustrated in FIG. 2A includes a natural gas source 220, a liquefied petroleum gas (LPG) storage tank 230, an enrichment control unit 210, an enrichment injector 240, and a mixing chamber 260.

The gas enrichment unit 200 may optionally include a gas characterization component 280 (as shown in FIG. 2B). The gas characterization component measures the properties of the natural gas source such as its heating value (BTU/cf), the moisture content, temperature, and pressure. The heat content or BTU/cf of the natural gas source 220 is continually compared to the optimum BTU/cf as calculated by the electronic control system 130. The enrichment control unit 210 dynamically determines the amount of BTU/cf enrichment of the natural gas source 220 that is needed so that the natural gas sent to the engine 110 equals the calculated optimal BTU/cf calculated for the optimal efficiency and combustion of the connected dual fuel engine 110.

The enrichment control unit 210 then instructs the enrichment injector 240 to inject a calculated quantity of a liquefied petroleum gas, having a known heat content that is higher than the heat content of the natural gas source 220, into a mixing chamber 260 containing the natural gas source 220 to create an enriched source of natural gas having the optimum calculated BTU/cf for delivery to the dual fuel engine 110.

The enrichment injector 240 is supplied with a source of liquefied petroleum gas (LPG) such as propane, butane, isobutane, pentane, or any combination of such gases. Commonly the LPG is supplied to the gas enrichment device 200 of transportation vehicles in a 5-20 gallon tank and to a field site from a site reservoir. The enrichment injector 240 may be an atomizer or a needle injector.

The gas enrichment unit 200 may also optionally include a flow control meter (FCM) 270 (as shown in FIG. 2B). The enrichment control unit 210 dynamically communicates with the electronic flow control meter 270 to ensure that the enriched natural gas in the mixing chamber 260 is delivered to the engine 110 at an optimum flow rate and pressure.

If the enriched natural gas delivered to the dual fuel engine has the optimal heat content for that particular engine under its specific operating conditions, the enriched natural gas will be maximally substituted for up to 70% of the diesel fuel. In addition, if the enriched natural gas-diesel mixture is optimal for the efficient running of that specific dual fuel engine and operating conditions, then the fuel combustion of the engine will be almost complete thereby minimizing the non-combusted methane natural gas emitted from the engine.

In one example, an engine running at an engine load of 25% (idling) when burning LNG with a BTU/cf content of 950-1050 BTU/cf had between 8-12% of the natural gas exhausted from the engine as non-combusted methane. In contrast, an engine of the same engine type and load condition burning a 1250 BTU/cf enriched natural gas only had between 2%-3% of the natural gas exhausted from the engine as non-combusted methane.

In another example, an engine running at an engine load of 30-35% when burning LNG with a BTU/cf content of 1040-1050 BTU/cf at a 26-28% substitution had about 30% of the natural gas exhausted from the engine as non-combusted methane. In contrast, an engine of the same engine type and load condition burning a 1400 BTU/cf enriched natural gas had a 68% substitution rate with only about 10%-11% of the natural gas exhausted from the engine as non-combusted methane.

Furthermore, an engine set at an engine load of 40-45% (typical of loads required of a field generator) fed an unenriched source of natural gas with a BTU/cf of 1050 produced an exhaust with about 21% non-combusted methane when the engine was run at a 30-40% NG substitution rate. On the other hand, a similar engine set at a similar engine load of 40-45% was fed an enriched source of natural gas with a calculated BTU/cf value for optimal efficiency (about 1120 BTU/cf) only produced an exhaust with about 3-4% non-combusted methane when the engine is run at a 30-40% natural gas substitution rate.

Yet another engine set at an engine load of 65-70% fed an unenriched source of natural gas with a BTU/cf of 1040 produced an exhaust with about 10% non-combusted methane when the engine was run at a 68-70% NG substitution rate. On the other hand, a similar engine set at a similar engine load of 65-70% was fed an enriched source of natural gas of 1400 BTU/cf only produced an exhaust with about 3-4% non-combusted methane when the engine was run at a 68-70% NG substitution rate.

The Natural Gas Enrichment Process

According to an embodiment, a process is disclosed for optimizing the natural gas caloric content and/or the fuel substitution ratio of a dual fuel engine in real time. The process may be computer-implemented. The optimization is typically based on the engine operating conditions, environmental conditions, the actual performance of the engine under the operating and environmental conditions, or a combination of such parameters.

The process involves providing a central processing engine such as the electronic control system 130. The electronic control system is configured to interact and communicate with both the engine sensor mechanism 120 integral to the dual fuel engine 110 and the gas enrichment unit 200. The central processing engine or electronic control system 130 may include control logic and a non-transitory computer readable storage medium.

The process involves transmitting actual engine data from the engine sensor mechanism 120 to the electronic control system 130. The engine sensor mechanism 120 may include a plurality of sensors for transmitting engine operating data. The engine sensor mechanism 120 may be configured to continually and dynamically monitor, measure and communicate the operating data of the dual fuel engine 110.

A dual fuel engine usually depends on diesel engine hardware. The base diesel engine may be modified in order to allow operation with relatively cheaper natural gas fuel. For example, natural gas fuel can be substituted for diesel fuel in varying proportions according to operating conditions. A dual fuel engine can operate with up to about a 70% fuel substitution ratio, that is, the fraction of total fuel energy contributed by natural gas, with the remaining coming from diesel fuel. Each engine has different fuel burn requirements in order for the engine to sustain a set power or load. For example, an older engine performs differently than a new engine.

FIGS. 3 and 4 are flowcharts illustrating a process for the optimal substitution of natural gas in a dual fuel engine in accordance with certain embodiments of the present invention. In certain embodiments, the process may be a computer-implemented process (e.g., executable on the electronic control system 130 as illustrated in FIG. 1). The electronic control system 130 may implement the process by acquiring real-time operational data from the system, evaluating the data against stored optimal engine performance data, and outputting appropriate control signals in the system such that an optimized fuel blend is fed to the engine.

As illustrated in FIG. 3, the process includes the step of continually monitoring engine operating data (block 310). The electronic control system 130 may implement the process at least partially by interfacing with a plurality of sensors distributed throughout the system. The sensors may be configured to dynamically measure, sense, and/or otherwise determine and generate a signal indicative of one or more engine operating parameters. As an example, the set of operating parameters may be associated with and/or may otherwise include a speed of the engine, a speed of a vehicle to which the engine may be connected, a load on the engine, a temperature of intake air directed to the engine via an intake passage, a temperature of ambient air, a temperature of exhaust emitted by the engine, combustion efficiency, cylinder head temperature, quantity of non-combusted methane, and/or other like operating parameters.

The electronic control system 130 typically includes one or more processing units (CPUs), one or more network interfaces, memory, and one or more communication buses for interconnecting these components. The monitored engine performance data can be continually retrieved and stored in memory. Memory includes high-speed random access memory, such as DRAM, SRAM, DDR RAM, or other random access solid state memory devices; and optionally includes non-volatile memory, such as one or more magnetic disk storage devices, optical disk storage devices, flash memory devices, or other non-volatile solid state storage devices. Memory optionally includes one or more storage devices remotely located from the CPU(s). Memory, or alternately the non-volatile memory device(s) within memory, includes a non-transitory computer readable storage medium. In some implementations, memory or the computer readable storage medium of memory stores the following programs, modules and data structures, or a subset thereof: an operating system that includes procedures for handling various basic system services and for performing hardware dependent tasks; a network communication module that is used for connecting the central processing engine to other computers via the one or more communication network interfaces (wired or wireless) and one or more communication networks, such as the Internet, other Wide Area Networks, Local Area Networks, Personal Area Networks, metropolitan area networks, VPNs, local peer-to-peer and/or ad-hoc connections, and so on.

The electronic control system 130 or a CPU included therein can map or relate the monitored engine operating data to predetermined engine performance data (block 320). This data can be used to determine the engine's fuel burn requirements. Diesel engines are designed to burn 100% diesel, but it is cheaper and reduces the environmental footprint to substitute natural gas for a certain percentage of the diesel. Each engine has a different fuel burn requirement in order for the engine to sustain a set power or load (an older engine performs differently than a new engine).

In some embodiments the predetermined engine performance data is obtained from the engine manufacturer and in other embodiments a CPU can nearly instantaneously map engine fuel burn requirements versus engine load for a specific engine. For example, at each load level experienced by the engine, the engine is initially fed 100% diesel. The engine can then be fed a set of fuel blends with natural gas substitution in an increment that is based on a predetermined optimal substitution ratio. At each load level of the engine, there is an optimum substitution of natural gas of a calculated BTU value that is needed to maintain the desired power level of the engine, maximize the substitution of natural gas for diesel and minimize the non-combusted methane. The CPU is configured to plot an actual fuel burn with the fuel blend with fuel burn with 100% diesel to determine the optimal substitution ratio. For instance, the natural gas substitution may be made in increments of 10%, and accordingly, the natural gas substitution is made at 10%, 20%, 30%, etc. The engine load, combustion efficiency and non-combusted methane may be calculated in nearly real-time along with an optimum caloric content of the natural gas (i.e., the optimal natural gas BTU).

The electronic control system 130 or a CPU included therein may include control logic that can utilize the mapped data to determine timing and quantity at which natural gas fuel should be injected into the air inlet manifold of the dual fuel engine and/or the optimal heating value of the natural gas that should be injected (block 330). The determination may be based on the engine speed, piston positions, engine load, intake temperature, air flow, cylinder head temperature and/or other engine operating parameters, as well as the one or more outputs demanded of the engine. The control logic will continually communicate the data analyzed by the electronic control system to the natural gas enrichment unit 200 (block 340).

The electronic control system 130 is in operative communication with the natural gas enrichment unit 200. The gas enrichment unit is provided upstream of the dual fuel engine. The gas enrichment unit 200 includes a natural gas source 220, a liquefied petroleum gas (LPG) storage tank 230, an enrichment control unit 210, an enrichment injector 240, a mixing chamber where the source natural gas and the injected LPG are mixed before being injected into the air intake manifold of the engine.

FIG. 4 is a flowchart of the natural gas enrichment process in accordance with certain embodiments of the invention. The enrichment control unit 210 dynamically determines the amount of BTU/cf enrichment of the natural gas source 220 that is needed so that the natural gas sent to the engine 110 equals the calculated optimal BTU/cf calculated for the optimal efficiency and combustion of the connected dual fuel engine 110 under its current operating conditions (block 410).

The enrichment control unit 210 then instructs the enrichment injector 240 to inject a calculated quantity of a liquefied petroleum gas, having a known heat content that is higher than the heat content of the natural gas source 220, into a mixing chamber 260 filled with the natural gas source 220 to create an enriched source of natural gas having the optimum calculated BTU/cf for delivery to the dual fuel engine (block 420). The enrichment control unit 210 may also communicates with an electronic flow control meter 270 to ensure that the enriched natural gas in the mixing chamber 260 is delivered to the engine 110 at an optimum flow rate and pressure (block 430).

The enrichment injector 240 is supplied with a source of liquefied petroleum gas (LPG) such as propane, butane, isobutane, pentane, or any combination of such gases. Commonly the LPG is supplied to the gas enrichment device 200 of transportation vehicles in a 5-20 gallon tank and to a field site from a site reservoir. The enrichment injector 240 may be an atomizer or a needle injector.

In one example, the control logic can dynamically control BTU content of the natural gas by opening a valve to a LPG storage tank and activating the enrichment injector 240 to inject a predetermined quantity of LPG into the mixing chamber filled with the natural gas source. After the natural gas is enriched, the valve to the LPG storage tank may be closed. In another embodiment, the enrichment injector 240 my include a valve used to access the LPG. On the other hand, if the actual parameters substantially match the desired parameters, the natural gas is not enriched since that is indicative of optimal engine performance.

The flowchart and block diagrams in the above figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.

It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

As will be appreciated by one skilled in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a non-transitory computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wired, optical fiber cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, as a stand-alone software package, partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).

The foregoing provides a detailed description of the invention which forms the subject of the claims of the invention. It should be appreciated by those skilled in the art that the general design and the specific embodiments disclosed might be readily utilized as a basis for modifying or redesigning the natural gas supply system to perform equivalent functions, but those skilled in the art should realized that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. A dual fuel engine natural gas enrichment unit including: a) a natural gas source having a known caloric value per cubic foot; b) a liquefied petroleum gas tank filled with a liquefied petroleum gas having a higher caloric value per cubic foot than the natural gas source; c) an enrichment injector; d) a mixing chamber; and e) an enrichment control unit in communication with the enrichment injector, wherein the enrichment control unit instructs the enrichment injector to inject a calculated quantity of the liquefied petroleum gas into the mixing chamber containing the natural gas source to increase the caloric value per cubic foot of the natural gas source to a desired caloric value per cubic foot; whereby the natural gas source is enriched to a calculated desired caloric value per cubic foot for injection into the duel fuel engine.
 2. The natural gas enrichment unit of claim 1 further including an electronic control system in communication with a dual fuel engine sensor and the enrichment control unit.
 3. The natural gas enrichment unit of claim 2 further including a flow control meter in communication with the enrichment control unit.
 4. The natural gas enrichment unit of claim 1, wherein the natural gas source is liquefied natural gas, compressed natural gas or pipeline gas.
 5. The natural gas enrichment unit of claim 1, wherein the natural gas source has a caloric value per cubic foot ranging from 950-1050 BTU/cf.
 6. The natural gas enrichment unit of claim 1, wherein the liquefied petroleum gas is propane, butane, isobutane, pentane or a mixture of the same.
 7. The natural gas enrichment unit of claim 1, wherein the enrichment injector is an atomizer or a needle injector.
 8. A natural gas supply and conditioning system for dual fuel engines including: a) a dual fuel engine that burns diesel fuel and natural gas having an engine sensor that monitors at least one engine operating parameter; b) an electronic control system in constant communication with the engine sensor, wherein the electronic control system calculates an optimum caloric value of a natural gas for substitution of a calculated amount of diesel for the dual fuel engine operating at a selected engine parameter; c) a diesel fuel supply; and d) a natural gas enrichment unit having (i) a natural gas supply, (ii) a tank of liquefied petroleum gas filled with a liquefied petroleum gas having a higher caloric value per cubic foot than the natural gas supply, (iii) an enrichment injector; and (iv) an enrichment control unit in communication with the electronic control system and the enrichment injector, wherein the enrichment control unit instructs the enrichment injector to inject a calculated quantity of the liquefied petroleum gas into a mixing chamber containing the natural gas supply to increase the caloric value per cubic foot of the natural gas source to the optimum caloric value per cubic foot.
 9. The natural gas supply and conditioning system of claim 8 wherein the engine sensor monitors a load on the engine, a temperature of intake air directed to the engine via an intake passage, an exhaust temperature, a combustion efficiency of the engine, a quantity of non-combusted methane emitted through the engine exhaust or a cylinder head temperature.
 10. The natural gas supply and conditioning system of claim 8 wherein the electronic control system includes a processing unit, a network interface, and a memory.
 11. The natural gas supply and conditioning system of claim 10 wherein the monitored engine operating parameter is retrieved from the engine sensor and stored in the electronic control system memory.
 12. The natural gas supply and conditioning system of claim 8 further including a flow control meter in communication with the enrichment control unit, wherein the enrichment control unit instructs the flow control meter to inject a set quantity of the enriched natural gas of the optimum caloric value per cubic foot into an air inlet manifold of the engine at a predetermined flow rate.
 13. The natural gas supply and conditioning system of claim 8 wherein the liquefied petroleum gas is propane, butane, isobutane, pentane or a mixture of the same.
 15. The natural gas supply and conditioning system of claim 8 further comprising a natural gas characterization component for measuring the natural gas supply properties and communicating the natural gas supply properties to the enrichment control center.
 16. The natural gas supply and conditioning system of claim 15, wherein the natural gas supply is pipeline gas.
 17. The natural gas supply and conditioning system of claim 15, wherein the natural gas supply has a caloric value per cubic foot ranging from 950-1050 BTU/cf.
 18. A method for regulating the natural gas used to fuel a dual fuel engine comprising: dynamically determining one or more engine operating parameters; mapping data related to the engine operating parameters with predetermined engine performance data to calculate an optimal natural gas caloric value and substitution ratio of natural gas to diesel fuel under a selected operating condition of the engine; enriching a natural gas source by injecting the natural gas source with a calculated quantity of liquefied petroleum gas to generate an enriched natural gas having the calculated optimal natural gas caloric value; and automatically injecting a desired quantity of the enriched natural gas into the dual fuel engine in accordance with the calculated optimal natural gas substitution ratio.
 19. The method for regulating the natural gas used to fuel a dual fuel engine of claim 18 wherein the enriched natural gas is injected at an optimum flow rate and pressure.
 20. The method for regulating the natural gas used to fuel a dual fuel engine of claim 18 wherein the optimal natural gas caloric value and substitution ratio of natural gas to diesel fuel is calculated by comparing the predetermined engine performance data of the dual fuel engine with real time operating performance data for the dual fuel engine.
 21. The method for regulating the natural gas used to fuel a dual fuel engine of claim 20 further comprising determining the optimal natural gas caloric value and substitution ratio of natural gas to diesel fuel needed to minimize an amount of non-combusted methane in the engine exhaust. 